The resolution of an optical system is typically limited by diffraction effects. Techniques aimed at achieving the super resolution deal with extending the resolution limit set by diffraction caused by the physical dimensions of the optics. Digital imaging provides for exceeding the limit set by a non-zero pixel size of a photodetector (e.g., CCD), i.e., the geometrical resolution.
Common geometrical super-resolution methods rely on the sub-pixel displacement of an image impinging on the detector, using mirrors. In these methods, it is assumed that the input does not change during the period of the scan. The scan itself is coined micro-scan. Afterwards, different sampled inputs are computationally combined and an enhanced picture is produced. These methods, however, suffer from several drawbacks, such as the need for mechanical elements that make the system more complex, costly and prone to malfunctions; and non trivial retrieval of the output, as it involves deconvolution of the output. Examples for such implementations are disclosed in the following publication: R. Riesenberg, Th. Seifert, A. Berka, U. Dillner, “Opto-micromechanical Super Resolution Detector System”, Proc. SPIE 3737, pp. 367-383, 1999.
Obviously, the above methods sacrifice a certain degree of freedom of the optical system. As indicated above, while the micro-scan is conducted, the input is assumed not to change. Therefore, the system temporal resolution has decreased in favor of enhanced spatial resolution. These super resolution methods sacrifice one or more of the systems' degrees of freedom in order to improve other degrees of freedom (such as spatial resolution). This is described in the following publication: Z. Zalevsky, D. Mendelovic, A. W. Lohmann, “Understanding superresolution in Wigner space”, J. Opt. Soc. Am., Vol. 17, No. 12, pp. 2422-2430, 2000.
Such known effect as aliasing is typically considered as a problem in the imaging techniques. This effect is associated with the following: Any attempt to capture image detail with a spatial frequency slightly greater than the Nyquist frequency (i.e., that of the photodetector pixel array) results in a spatial or dimensional distortion of that detail, i.e. individual image points are stretched, shrunk, or displaced to fit the pixel array, and if such fine detail covers any appreciable area, then visible aliasing occurs. Practically, aliasing occurs when the image resolution is more than half of that of the detector (Nyquist sampling rate). In mathematical terms, aliasing occurs when the following condition takes place: 2Δvimage>Δv, wherein 1/Δvimage is the image resolution measured on the detector plane, and 1/Δv is the detector resolution, Δv=1/Δx, Δx being the pixel pitch of the detector. As indicated above, aliasing effect is considered as a problem in imaging techniques, and various techniques are typically applied to reduce this effect.